On carrying out the static surveying using GPS for local control at forest, it is very useful to know how much of the signals will reach the antenna after penetrating tree canopy. The objective of this study is to determine the observation periods in consideration of signals weaken by tree canopy using the sky photograph as full-frame fisheye image with picture angle of 180 degrees and the ephemeris of satellites at observation point. The collected data at the point were the observation time, the sky coordinates and the signal strength of each satellite. We related the possibility of signal penetrating tree canopy to the luminance ratio of each pixel to neighboring sky pixel using the digitized sky photograph. Regression analysis of the collected data shows that there is a very straight relationship between the signal strength and the elevation of satellite under no satellite obstruction and a linear formulation is justified. Also it shows that there is a relationship between the estimated signal strength with elevation of satellite to observed signal strength ratio under some satellite obstructions with tree canopy and the luminance ratio at the sky coordinates of satellite. Then, in method using these relationships we could presuppose how much of the signals would reach the antenna after penetrating tree canopy and determine the observation periods. This procedure is built in a computer program called EYE.

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It is important that damages to the natural environment around the forest road should make smaller. However, now the location of such roads (the ecoroad) needs a lot of work and much time. We examined the location of ecoroads by the method of the simple image processing. We picked out areas that need an attention when constructing ecoroads using the digital orthophoto, DTM and the contour map. Overlaying those areas, we zoned areas where construction of forest roads is restricted. Considering a lot of factors in the forestscape, we could locate the ecoroad in the forest easily.

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Two methods of removing a hung-up tree manually in early thinnings of Cryptomeria japonica were investigated: pulling down a hung-up tree to the felling direction with a wire rope (method A) and rotating down the trunk with it (method B). The average resistance force acting on the crown of a hung-up tree for method A and method B was 30.0kgf and 14.1kgf, respectively. The resistance force caused by the deflection of branches and the trunk might be larger for method A than for method B. Furthermore the average resistance moment acting on the crown of a hung-up tree was much larger for method A (193.5 kgf・m) than for method B (4.2 kgf・m) because the moment arm from the center of the rotation to the line of action of the resistance force was much longer for method A. In conclusion, it is effective to use a light subsidiary tool such as a long pole with a hook for pulling down a hung-up tree at a higher position or a short lever for rotating down it.

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Line thinning by a high-performance logging system is believed to be an effective solution to thinning depressions. This study examined the damage caused to a residual stand through the introduction of a harvester-forwarder system into a line thinning test site where row numbers for felling differed. The rate of damage for 1-row-felling/3-row-residual system was 10.7%, and for a 2-row-felling/5-row-residual system was 32.6%. Ninety-three and two-tenths percent of the damage occurred in the harvester process, while two-thirds of the damage occurred in bucking. Slight damage to sapwoods was found to be 77.3%, with heavy damage at 4.5%. The relationship between thinning tree size and injury rate appears clear. Two-thirds of the damage in the region took place at a height of one meter or less, and two-thirds of the damaged areas were 50 cm^2 or smaller. The rate of damage rate appears to be affected to a great extent by the size of the thinning tree and the thinning tree number and rate.

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